Sounds fishy to me...

If you were to dangle an underwater microphone into the koi carp pond at Kew Gardens, you might be surprised how much sound is picked up. In other words, the underwater realm is a noisy place, and the sounds you hear there can be a giveaway for who’s around and in what sorts of numbers. That, in turn, can be used to gauge the health of the local ecosystem, and scientists want to build a global reference library of these sounds. Evelyna Wang caught up with Exeter University’s Sophie Nedelec to hear what she’s got in mind…

Sophie - There are so many animals that make sounds underwater - it's incredible. All of the mammals that live in the water make sounds, we believe, so that's about 126 mammal species. There's about 34,000 fish species that live in the water. And so far we know that at least a thousand of those make sounds, but the real number is likely more. It's just that we haven't found them yet. And then there's about 250,000 known marine invertebrates, and out of those, we know of at least a hundred that make sounds as well.

Evelyna - I understand how whales and dolphins and seals can make sounds, but how do fish and invertebrates do it?

Sophie - So fish have incredible ways of making sounds. Many fish have a sonic muscle, which they can vibrate or drum onto their swim bladder. It's like a little bubble of gas that's inside their bodies. So we have plainfin midshipman fish that produce a kind humming sound as their love song. Other fish rub their teeth together such as clownfish, like in the film 'Finding Nemo'. And then in terms of the byvalves you can often hear a kind of clacking and shuffling, which comes from the shells knocking together as well.

Evelyna - Even oysters make sounds. I never knew. So you have all of these recordings, what can you learn from them?

Sophie - So all of these sounds can be really useful to monitor where there are areas of healthy habitat or where there are areas where habitats might be shifting in their distribution due to climate change or maybe deteriorating in quality. So snapping shrimp, for example, are very small, but they make one of the loudest sounds that comes out of any animal under the water. They make a snap by clacking together two parts of one of their claws and their claw shuts so quickly that it actually creates a cavitation bubble and that bubble snaps shut with so much force that it momentarily creates energy that's as hot as the surface of the sun. So these shrimp can actually be really useful because they tell us about the health of a coral reef, as well as just, you know, that they're there being shrimp. So the healthier a coral reef is the more of these snapping shrimp sounds that we can find and also the more fish vocalizations that we find as well.

Evelyna - So Sophie, you are part of the team trying to establish this global library of underwater biological sounds. What are the main goals of this project?

Sophie - What we really want to call for is a global level of library, where these sounds are being shared around the world. And that will mean that it's open access so that anybody can contribute to it and anybody can use it. We need now more than ever to be able to catalogue what animals can be found in the ocean and where they can be found as we are losing biodiversity at alarming rates. And to involve citizen scientists in this effort as well. So if a person is to make some sound recordings under the water, then they might be able to upload it to the library and that would help identify what species people are encountering. I think the underwater world often can suffer from an out-of-sight-out-of-mind problem when it comes to engaging with it and protecting it. But this could be a way for an average person to engage more in their local blue habitats.